1,1,2-Trichloro-1,2,2-trifluoroethane ("113") and 1,1,1-trichloroethane ("140a") are used as cleaning solvents in applications where they are applied to the part to be cleaned and allowed to evaporate. As these solvents are suspected of depleting the ozone layer, it is desirable, when cleaning in an open environment, to find an alternative solvent with a lower ODP, preferably below 0.1. Some cleaning applications can be setwed by aqueous cleaners, but they are slow to evaporate and can cause corrosion if not completely removed. Hydrocarbons, alcohols, or other organic solvents can be used for cleaning and will evaporate at a practical rate, but they are flammable and can not be used for many cleaning applications performed in an open environment. Thus, 113 and 140a are the only available nonflammable cleaning solvents with an acceptable evaporation rate (that is, as noted above, a rate slow enough for the solvent to have time to clean and drain off the pan to be cleaned, but fast enough so that in an open environment work is not delayed by waiting for the solvent to evaporate).
Pure chlorinated solvents such as perchloroethylene ("PCE") or trichloroethylene ("TCE") are too toxic for such evaporative cold cleaning applications performed in an open environment.
Pure 1,1-dichloro-1-fluoroethane ("141b") is a good solvent, but it is not suitable for the evaporative cleaning applications of this invention because of its low boiling point (31.degree. C.) and large heat of vaporization. The low boiling point causes the 141b to evaporate very quickly in an open environment such that it will evaporate before it can carry the soil off the part to be cleaned. This, combined with the high heat of vaporization, causes cooling of the part to be cleaned, so that water can freeze out of the atmosphere, causing frost to form on the part. When the frost melts, it leaves water, which can cause corrosion on metal parts, or interfere with following uses of the cleaned part.
Several patents have been published recently on azeotropic or near azeotropic solvent blends of 141b and alcohols, such as EPC Application 325,365 and U.S. Pat. Nos. 4,836,947 and 4,842,764, but these patents do not disclose the use of a third, nonflammable, component to ensure that upon evaporation neither the vapor nor the liquid fractions will have a flash point. ("Flash point" is measured by ASTM method D56 and is the temperature, if any, at which a flame passed over a cup of liquid will ignite the vapors so that the flame spreads down and outward. 141b is an example of a compound with no flash point.) Further, such azeotropic blends have over about 90% 141b and a boiling point below that of 141b, so that they suffer from the same deficiencies as pure 141b.
Combinations of 141b with chlorinated solvents (or alcohols) such as PCE have also been disclosed (as in Japanese Patent 1-132814). While chlorinated solvents such as PCE and TCE can be used to somewhat lower the concentration of 141b, a manufacturer of these solvents (Dow) recommends limiting their use to levels of no more than about 25% because of their toxicity.